Differential reciprocating hydraulic motor



May 12., 1970 F. B. FISHBURNE 3,511,130

DIFFERENTIAL RECIPROCATING HYDRAULIC MOTOR 4 Sheets-Sheet 1 Filed April 25. 1967 May 12, 1970 F. B. FISHBURNE 3,511,130

DIFFERENTIAL RECIPROCATING HYDRAULIC MOTOR Filed April 25, 1967 4 Sheets-Sheetl 2 /V/v///////\//V//////V// Va* INVENTOR Francis B. Fshburne ,/fmmfwyo/w ATTORNEY May 12T, 1970 F. B. FISHBURNE 3,511,130

DIFFERENTIAL RECIPROCATING HYDRAULIC MOTOR Filed April 25, 1967 4 Sheets-Sheet 4 FAST PB-l SLOW FoRIvARD Q LQ. FORWARD /83 VALVE c 85 '09 |05 vALvE A MANUALq H YW RETURN 86 86 |07 '06 vALvEB [lol 2me HYDRAULIC LINE Ls.| IDI o"tct93 L Ils I RETURN /ll4 SIGNAL AUTOMATIC RELAY SELF HOLDING RETURN (THRU PD2. LSI AND JUMPERI FIC-3.10.

INVENTOR Francis B. Fshburne ATTORNEY United States Patent C U.S. Cl. 91-31 11 Claims ABSTRACT OF THE DISCLOSURE The reciprocating motor is capable of many uses, but is described as used for pushing kiln cars through a kiln for burning brick. Two hydraulically independent pumps, driven by a common electric motor are employed. One of these pumps delivers motive fluid through a metering valve simultaneously to both sides of the differential piston to produce a slow, uniform working stroke. Means are provided, including the other pump and a manually controlled valve, for supplying motive fluid at a higher rate, independent of said metering valve, to both sides of said piston, to produce a relatively fast forward stroke when dseired. Means are also provided, including said second pump and suitable remote controlled valve means independent of said metering valve, for producing a rapid return stroke to the starting position of the parts. The remote controlled valve means may be actuated either manually, or automatically at the end of each working stroke to produce the rapid return stroke.

This invention relates to hydraulic power systems and more particularly to a system for controlling a reciprocating hydraulic motor.

Although applicable generally to motor cylinders operating presses and other things, the invention has particular utility when applied to horizontally disposed cylinders used for pushing heavy loads, as, for example, pushing brick cars through a kiln in a brick manufacturing plant, and the invention will be described in connection with such a brick car pusher.

In equipment of this kind it is desirable to have an initial fast forward movement of the pushing element under no load until it engages a car, then a very slow movement as the motor element pushes the loaded car through the kiln, and finally a rapid return stroke as the motor element moves back to its starting position, thus completing the cycle.

The sequence has heretofore been accomplished by employing an ordinary double acting cylinder with suitable control valves having a piston provided with the usual packing.

It is of the utmost importance to maintain the slow, scheduled pushing movement at a uniform speed throughout the working stroke, and during successive working strokes, so that the time of exposure to the heat (usually gas flames) of all portions of the car load, and of each successive car load as it moves through the kiln will be the same, so as to properly burn the brick.

The problem that has for many years plagued the industry is that it has been found impossible, with thn available equipment, to maintain a uniform speed at all times during the slow scheduled push or working stroke, or during successive working strokes. This ha" been due, for one thing, to unavoidable leakage developing at the piston packing.

I have discovered that this problem may be solved by converting the double acting motor cylinder at least during the working stroke, to a differential piston motor arrangement, in which the same pressure is applied simultaneously to both sides of the piston. With such ICC an arrangement, there is no tendency for motive fiuid to leak past the piston.

Another thing that has contributed to the difficulty of maintaining a uniform slow speed during the timed push or working stroke is leakage in the control valve or valves. Spool type four-way valves have usually been employed, and these gradually become worn, permitting fluid to escape past them.

I have discovered that this problem may be solved by eliminating the spool type valves and using instead so-called poppet type valves, properly connected and controlled. This type of valve is leakproof.

The general object of the present invention is therefore, to devise a motor cylinder and control means therefore, in which provision is made for a fast approach to a slow scheduled pushing stroke, and a rapid return stroke, and in which the speed of travel during the slow working stroke is maintained absolutely uniform.

To this end, an ancillary object of the is to provide means for converting, at least through the working stroke, the double-acting motor cylinder to a differential piston arrangement.

In order that the invention may be readily understood, reference is had to the accompanying drawings, forming part of this specification, and in which:

FIG. l is a view showing a longitudinal horizontal section the general arrangement of the improved differential piston motor, and showing diagrammatically the novel pump system and control valves therefore;

FIG, 2 is a longitudinal section through one of the air-actuated, solenoid-operated control valves which I employ;

FIG. 3 is a plan view of the rear end portion of my improved hydraulic motor pusher cylinder showing the dogs or latches which engage the kiln cars;

FIG. 4 is a side elevation thereof, parts being in section;

FIG. 5 is a plan view, on a smallerscale showing the pusher cylinder, the transfer car, several kiln cars, and a portion of the kiln itself;

FIG. 6 is a side elevation of the same showing the parts in one piston;

FIG. 7 is a similar side elevation, but showing the parts in a different position;

FIG. 8 is a side elevation of the transfer car, looking in a direction at right angles to FIG. 6;

FIG. 9 is a plan view, on a smaller scale, showing the transfer car and track, several storageI tracks, kiln cars on said tracks, and the kiln itself, as well as the location of the hydraulic pusher cylinder; and

FIG. l0 is a diagram showing the electrical circuits by which the various control valves may be operated.

Referring to the drawings in detail, and more particularly first to FIGS. 5, 6 and 8, the brick plant comprises an elongated, gas-fired kiln 1 through which extend track rails 3, on which rails run kiln cars 2. The cars, loaded with green brick, are propelled through the kiln by means of my improved differential hydraulic motor 4, located between the track rails.

In reciprocating hydraulic motors comprising a cylinder and piston, it is immaterial, from a theoretical standpoint whether the piston or the cylinder moves, while the other is held stationary, but there are practical advantages, in my improved design, in having the piston fixed, and the cylinder movable, so in the drawings I have illustrated such an arrangement.

The movable cylinder 4 is supported on two pairs of wheels 13 and 13', each pair being mounted on an axle 12 and 12', the wheels being adapted to travel along `track rails 5, disposed between the car rails 3 (see FIG. 5).

Adjacent one end of the track rails 3 and disposed at right angles thereto are a pair of rails on which the wheels 9 of a transfer car 8 travel. The kiln cars 2, loaded with green brick, accumulate on storage tracks 11, and as is well known, the transfer car 8 functions to pick up one at a time, the loaded kiln cars from the storage tracks 11, and move them to the position shown in FIG. 5, where they can be rolled oif of the transfer car 8 on to the tracks 5, and thence into the kiln.

It may be mentioned here that in co-pending application Ser. No. 608,125, now Pat. No. 3,450,059, filed Jan. 9, 1967 by Fishburne and Waldrop, there is shown a View very similar to FIG. 9. However, the operation in that case was just the reverse of that of the present case. In the prior case the purpose was to remove car loads of burnt brick from the kiln and distribute them onto storage tracks, while in the present case the purpose is to fe'ed car loads of green brick into the kiln.

Pivotally mounted on the axle 12 of the cylinder structure above described is a car-pushing dog or latch. This comprises a pair of arms 15 connected at their outer ends by a cross-bar 15a. It can swing from an inoperative position, shown in dotted lines, up to the operative position shown in full lines, the swinging movement being limited by a stop 16.

As best shown in FIG. 1, a ring 17, associated with a packing gland, surrounds and projects radially outward from the cylinder, and rigidly secured to this ring as by welding, are a pair of arms 18 extending parallel with the cylinder. At the free end of these arms is pivoted, as at 20, another dog or latch comprising arms 19 united at their ends by a cross bar 19a, the swinging movement being limited by a stop 19'.

The dogs 15 and 19 are urged upwardly against the stops by tension springs 15b and 19h, secured to the lower ends of the dogs.

Referring now to FIG. l, inside the movable cylinder 4 is a fixed, hollow piston rod 21, to one end of which is secured a piston 22. Because of the differential action, with the same pressure on both sides of the piston, as hereinafter described, no piston packing is required when the piston is used differentially. However, to prevent leakage during the return stroke, as hereinafter described, I prefer to employ V-packing 23, turned to make a seal for one direction only.

The other end of the piston rod 21 is secured to a block or fitting 24, mounted as by means by a clamping nut 25 on a xed plate 26 fastened to the rails 5, or other stationary support. This block 24 is formed with two axially extending openings 27 and 28. A motive fluid supply pipe 29 is fitted into the opening 27, and a second motive fluid supply pipe 30 is fitted into the outer end of the opening 28. From the inner end of this opening extends a pipe 31 inside of the fixed hollow piston rod to an elbow 32 which discharges laterally through an opening 33 in the wall of the hollow piston rod into the space 34 between the rod and the cylinder. An opening 35 extends longitudinally through the piston 22 and establishes communication between the inside of the hollow piston rod 21 and the space 36 between the piston and the closed end ofthe cylinder.

At the other end of the cylinder is a packing gland surrounding the piston rod and comprising lantern gland packing 37, held by a screw cap 38, in the usual manner. Such packing is substantially leakproof, but in order to detect any possible leakage, I connect to the gland a drain line 37a extending to the tank, and having interposed therein a sight glass 37b.

In connection with the supply and exhaust of motive fluid to and from the cylinder, I employ three airactuated electrically-operated control valves. These are indicated in FIGS. l and l0 at A, B, and C, and the details of one method of constructing such valves are illustrated in FIG. 2.

By references to this gure, it will be seen that the valve comprises an elongated body 40, preferably vertically disposed, in which reciprocates a valve member 41. The upper end of this valve member 41 is secured to a horizontal plate 42. This plate can move up and down within an enlarged chamber formed of a bottom piece 43, integral with the body 40, and a top piece 45, bolted together around their edges. Interposed between the pieces 43 and 45 is a flexible diaphragm 46, resting on the plate 42. This plate is supported on a compresion spring 44, interposed between it and the bottom piece 43.

Mounted on the top piece 45 is an electrically controlled air valve 47, having a pipe 48 connected with a source of compressed air, and an exhaust pipe 49. The valve is operated by a solenoid indicated diagrammatically at 50, and supplied with current by wires 51.

I have not attempted to illustrate the exact details of this solenoid-operated air valve, as such devices are well known in the art, and are commercially available, as, for example, from Bellows Valvoir Company, Akron, Ohio.

The body 40 of the motive fluid control valve has at opposite sides inlet and discharge connections 52. and 53. The valve member 41 is formed with longitudinally spaced portions 54 and 55 of reduced diameter, and between these portions is a beveled portion 56, arranged to engage a similarly beveled seat 57, formed on the body 40, Ibetween the inlet and outlet ports.

If the valve is of the normally closed type, the parts occupy the position shown in full line in FIG. 2, the two beveled portions 'being in close engagement. In this position it will be seen that the higher the pressure on the inlet side, the more tightly will the Ibeveled surfaces be pressed together. Thus, the design provides a practically leakproof valve.

When it is desired to open the valve, current is supplied to the solenoid winding 50. This results in admitting air into the space above the diaphragm 46, thus depressing this diaphragm and the plate 42, compressing the spring 44, and moving the valve member 41 down to the position indicated in broken lines. In this position, the beveled surfaces are separated, and motive lluid may flow freely from the inlet to the outlet. When there has been suicient flow, the circuit to solenoid 50 is broken, and suitable spring means inside the air valve (not shown) shuts off the supply of air and opens the exhaust, thus venting the air from above the diaphragm, and permitting the spring 44 to bring the beveled surfaces into engagement again, thereby closing the valve.

As more fully explained hereinafter, some of the valves A, B, and C are normally closed, while others are normally open. When it is desired to maintain normally open a valve such as illustrated in FIG. 2, the air valve has to be arranged so that, when the solenoid is deenergiz/ed, the exhaust is closed, and air pressure admitted behind the diaphragm to hold the Valve member 41 in the position shown in broken lines, and when it is desired to permit the valve member to return to closed position, the solenoid is energized to shut olf the supply of air and open the exhaust. Thus in one case, the solenoid is energized to open the valve, and in the other case, the solenoid is energized to close the valve. It is believed the detailed arrangements of the solenoid-operated air valve to accomplish either desired result will be obvious to those skilled in the art, and it is thought that no further explanation is necessary.

1Referring again to FIG. 6, one of the kiln cars 2 is shown as carried by the transfer car 8 in position to be pulled olf. This pullling off is accomplished by the dog or latch 19 engaging behind a member 6 on the kiln car. Then, when the cylinder 4 moves forward, as indicated by the arrow, the kiln car will be pulled off of the transfer car onto the tracks 3, and into the kiln, the dog 19 moving to the position shown in broken lines in FIG. 6. Thus the cylinder must have a stroke more than twice as long as the length of a kiln car. In practice, I have -used kiln cars about 7'6" long, rwith a cylinder having a stroke of approximately 19. The two dogs are spaced some 2 apart, and the transfer car tracks have been so located that the distance from the front of a kiln car, mounted on the transfer car, to the entrance of the kiln is the length of a kiln car plus about 2 or, in other words, around nine and a half feet.

After the dog 19 has pulled a kiln car off the transfer car into a position just inside of the kiln, as shown in FIG. 6, the cylinder makes a return stroke far enough to enable the dog to engage behind the rear end of the car which the dog 19 has just pulled in, and push it, and all cars ahead of it, on through the kiln, as illustrated in FIG. 7. In this gure, the cylinder is shown as having traveled a substantial distance along the piston rod, so that the rod 21 projects far beyond the cylinder.

In the introduction, I have spoken of providing means for producing a fast forward movement or approach, before the slow scheduled push begins. This fast forward movement would be used during the time the cylinder is pulling the car off of the transfer car, and brin-ging it up into the kiln, as shown in FIG. 6. Also it may be used in moving the last kiln car over the space of two feet or so separating the two cars, as shown at the left in FIG. 6.

Once the cars are in Contact, however, the relatively fast movement is discontinued, and all further forward movement will be `at the very slow rate required for the timed or scheduled push. At the end of this forward stroke, it returns to its initial position as shown in FIG. 6 to engage and pull off another kiln car (assuming that the transfer car, carrying another kiln car has meanwhile been moved into position).

Still referring to FIG. 1, my improved hydraulic system comprises a tank 58 containing the motive fluid and a motor 59 coupled directly to two rotary pumps 60 and 61. Intake pipes 62 and 63 extend from the pumps down into the tank, and are shown as equipped with lters 64 and 65 at their ends.

From pump 60 extends a pipe `66 to a metering valve 68, an adjustable relief valve 67 being interposed in this pipe, with a return pipe 67a extending back into the tank.

This metering valve is in the nature of a restricting or throttling device that can be adjusted to regulate the flow through it as desired. By closing it to a greater or less extent, the ow may be throttled down to a relative small volume, thus producing the timed or scheduled slow movement of the cars through the kiln, as hereinafter described.

From the other side of the metering valve 68 extends a pipe 69, having a check valve 70` in it, to the pipe 29, which, as above described, communicates with the interior of the hollow piston rod 21. This pipe 29, at a point beyond its junction with pipe 69, connects with the inlet side 52 (FIG. 2) of valve B. A drain pipe 71 extends from the outlet side 53 of this valve back to the tank 58.

From the pump 61 extends a pipe 72, to the pipe 30, which as above described, communicates with the space 34 between the piston rod and cylinder, this pipe 72 having interposed in it a check valve 74 and a relief valve 73, from which extends a drain pipe 73a back to the tank.

Pipes 75 and 76 connect the opposite sides of valve A with the pipe lines 72 and 69, respectively.

A pipe 77 taps pipe 72 at a point adjacent the pump 61, and delivers into the inlet side of valve C. A discharge pipe 78 extends from the outlet side of this valve back to the tank.

In FIG. 10 I have shown the simple electric circuits used to control the operation of my improved hydraulic motor.

The two sides of the line are indicated at 80` and 81, the latter being grounded. I employ two push button switches PB-l and PB-2, and a relay R-l. So much for the manual control, and I have shown, combined with this manual control an automatic return control, so that,

after making its working stroke the movable part of the motor, i.e., the cylinder, can be arranged to be returned to its initial position either manually or automatically, as desired.

For the automatic return, I employ a second relay R-Z, a limit switch LS-l, and a pressure switch PS-1.

OPERATION The valve B is normally closed, as shown in full lines in FIG. 2, while the valves A and C are normally open, as shown in broken lines. Thus energization of the solenoid 50 serves to open valve B, but to close valves A and C.

Assuming that none of the solenoids are energized, but that the motor 59 is energized, driving both pumps, the operation is as follows. Valve C being open, the fluid delivered by pump 61 is returned to tank through valve C and pipes 77 and 78. In other words, this fluid idly circulates.

The fluid delivered by pump 60, on the other hand, flows up through pipe 66, metering valve 68 and pipe 69 to pipe 29. Valve B being closed, this iluid is forced through pipe 29, hollow piston rod 21 and opening 35 into the big end of the cylinder, i.e., the space 36 between the piston 22 and the end of the cylinder. At the same time, by reason of the valve A being open, fluid ows through pipes 76 and 75 into pipe 30, from which it passes through pipe 31 and opening 33 into the space 34 between the cylinder and the rod 21, i.e., the rod end of the cylinder. Thus the same fluid pressure is simultaneously applied to both sides of the piston, so that there is no tendency for the uid to leak past the piston. The pressure being the same, the force applied to the side of the piston at the big end of the cylinder predominates, because of the difference in the effective areas on which the pressure acts. Thus the cylinder moves forwardly or toward the left, as viewed in FIG. 1, and as indicated by the arrows in FIG. 6.

As this movement takes place, since valve A is normally open, the fluid contained in the rod end of the cylinder is transferred, through pipes 75, 76 and 69 to pipe 29, and thence to the big end of the cylinder.

The speed of the forward movement is regulated by adjusting the metering valve 68 as desired, to produce the timed or scheduled push. Since the metering valve acts to restrict the volume of fluid flow to a relatively small amount, and since this small amount is divided between the two sides of the piston to produce the differential action, as above described, the scheduled rate of movement is relatively slow, so as to allow the cars to remain in the kiln the length of time necessary to assure proper burning of the brick.

If it is desired to speed up the forward movement during any portion of the stroke before the pusher dog engages the car or string of cars, the operator depresses push button PB-l. Current will then ilow through contacts 82, wire 83 and winding `84 of the solenoid of valve C, thus closing this normally open valve. Motive uid delivered by pump `6'1 will then be forced to flow unrestrictedly up through line 72 and through pipes 75 and 76, and normally open valve A into the big end of the cylinder through pipe 29. This causes the cylinder to move rapidly. When this fast forward movement has gone far enough, the operator releases push button PB-l, thus causing valve C to open again. Then the slow scheduled movement proceeds.

When the cylinder approaches the end of its forward stroke, it, of course, must be returned to its initial starting position. Referring first to the manual return, the push button PB-2 has a pair of Off contacts 85 and a pair of on contacts 86. These on contacts are connected by wires 101 and 102 to the above mentioned relay R-l. This relay is of a well known standard type, the same as illustrated in my prior Pat. No. 3,118,512, dated Jan.

21, 1964, and comprises a panel having a row of contacts 89, 90 and 91 at one end a row of terminals 92, 93, 94 and 95 at the other. It has a coil 96 connected between terminals 92 and 95, and a pair of jumpers 97 and 98, connecting terminal 93 with terminals 92 and 94.

Pivotally mounted at one end on terminals 93 and 94 are a pair of armatures 99 and 100, the other ends of which normally rest against dead contacts 90. When the coil 96 is energized, these armatures move outwardly and engage contacts 89 and 91. The wire 102 connects with terminal 92 and one end of the winding 96, while the other end of this winding is connected by wire 103 to the other side 81 of the line.

Contact 89 is connected to wire 104 with wires 105 and 106, in parallel, leading through solenoid windings 107 and 108 of valves A and B, respectively to the other side of the line.

Contact 91 is connected by wire 109 to Wire 83, leading to winding 84 of valve C.

When it is desired to use the manual return, the operator depresses push button PB-2, thus bridging the contacts `86 and feeding current through wires 101 and 102 to the coil 96 of relay R-l. This causes the armatures 99 and 100 to engage contacts 89 and 91. Current the-n flows from wire 102 through jumper 97, armature 99 and wire 104 through solenoid windings 107 and 108 of valves A and B respectively. 'This closes valve A and opens valve B. At the same time, armature 100 engages contact 91 and feeds current through jumper 98 and wire 109 through solenoid winding 84 of valve C. This closes valve C. So valves A and C are closed, and valve B open.

Opening of valve B permits discharge of the contents of the big end of the cylinder back to tank. Closing of the valve C results in the pump 61 forcing motive fluid up pipe 72, and since valve A is closed, blocking may iiow through pipes 75 and 76, this iiuid is delivered through pipe 31 into the rod end of the cylinder, thus causing the return stroke. And it will be noted that this flow of motive iiuid into the rod end of the cylinder is not through the metering valve but comes freely and unrestrictedly direct from the pump 61. Thus the return stroke takes place at relatively high speed. It will be further observed that while the forward or working stroke of the cylinder takes place under differential action of the lluid on both sides of the piston, the return stroke is produced by applying motive uid to one side of the piston only.

As above mentioned, in addition to the manual return means, I have provided an automatic return. This is arranged to be triggered by a switch operated by the increased pressure of the fluid as the cylinder reaches the end of its forward stroke.

For the automatic return, I utilize a second relay R-2, and a limit switch LS-l, in addition to the pressure switch PS-l. The relay R-2 is substantially similar to R-I, and the same reference numerals have been used to designate corresponding parts.

The limit switch comprises a member 88- co-operating with a pair of contacts, one of which is connected by wire 87 to one of the off contacts 85 of push button PB-Z, while the other contact of the limit switch is connected by wire 111 with contact l89 of the relay. The pressure switch comprises a pair of contacts 110 arranged to be bridged by a switch member moved one way by the pressure, and the other way by a spring 115. One of the contacts 110 is connected to the line 80, and the other is connected by wire 112 with terminal 92 of the relay. Another wire 116 connects the line 80 with terminal 94 of the relay.

The operation is as follows:

When the pressure switch closes, current flows from line 80 through Winding 96 to the other side of the line, thus energizing the relay. At the same time, current flows from the off Contact 85 of push button PB-2, through wire 87, limit switch 88, Wire 111, contact 89, armature 99 and jumper 97 through the coil 86, thus making the relay self holding. Meanwhile, current ows through wire 116, armature 100, contact 91 and wire 101, to and through the winding 96 of relay R-l. This energizes this relay, causing it to supply current to the windings 84, 107 and 108 oi the valves C, A and B, producing the resuits described above. The return stroke continues until a projection, properly placed on the moving cylinder, trips the limit switch, thus breaking the holding circuit of relay R-Z, and restoring the system to its initial condition.

Preferably I provide an audible or other signal 114, to indicate when the cylinder has been returned. This is connected by wire 113 with the terminal 93 of relay R-Z.

What I claim is:

1. A hydraulic power system for controlling a difierential reciprocating motor having a rod en and a big end, associated with a load requiring a low speed working stroke in combination with a rapid return stroke under no load, comprising a source of motive uid under pressure; a metering valve; a second valve; means for delivering the motive fluid through said metering valve directly to said big end, and, at the same time, through said second valve when open to said rod end to produce the low speed working stroke; valve means for venting said big end; a second source of fluid under pressure; and means for delivering motive iiuid under pressure from said second source unrestricted by said metering valve directly to the rod end only of the motor with said second valve closed, rwhile venting the big end, to produce the rapid return stroke.

2. A system in accordance with claim 1 in which a rapid advance stroke under no load as well as a rapid return stroke is required, and in which means are provided or directing motive uid unrestrictedly and freely to both sides of the piston to produce the rapid advance stroke of the piston.

3. A system in accordance with claim 1, in which the motive iluid is delivered under pressure from two pumps driven by a prime mover and in which means are provided for directing the output from one pump through said metering valve to both sides of the piston to produce the slow speed working stroke, and in which means are provided for directing the output from the other pump unrestrictedly to the rod end only of the motor to produce the rapid return stroke.

4. A system in accordance with claim 3 in which a rapid advance stroke under no load, as well as a rapid return stroke is required, and in which means are provided for simultaneously directing the combined outputs from both pumps to opposite sides of the piston to produce the no load rapid advance of the piston.

5. A reciprocating hydraulic motor comprising a differential cylinder and piston, a metering valve, and means for delivering motive iluid through said valve at the same pressure to both sides of said piston simultaneously, and a control Valve in addition to said metering valve for directing the iow of motive uid from said metering valve into and out of said cylinder, said control valve being of the poppet type and comprising a reciprocating valve member having a beveled portion engaging a beveled seat, whereby, when said valve is closed, the possibility of leakage is substantially eliminated.

6. In a hydraulic power system for controlling a diierential reciprocating motor, a first source of motive fluid under pressure, a metering valve, a second valve, means for directing a restricted ow of fluid from said source through said metering valve directly to said big end and at the same time through said second valve to said rod end to produce a relatively slow forward stroke, a second source of motive uid under pressure, means for venting said big end, and means for delivering a ow of motive uid from said second source, unrestricted by said metering valve, to the rod end of said motor to produce a relatively ast return stroke,

7. A system according to claim 6 wherein said second valve is closed during said fast return stroke.

8. A ditferential reciprocating hydraulic motor connected with a load requiring an accurately timed movement at a speed which is relatively low and substantially constant throughout the working stroke and uniform during successive working strokes, said motor comprising a xed piston and a cylinder movable over the same, said piston comprising a big end and a rod end, a hollow piston rod on one end of which said piston is mounted, a pair of uid delivery pipes secured to the other end of said piston rod, said pipes being connected with independent sources of uid under pressure, one of said pipes communicating with the interior of said hollow piston rod, said piston having an opening establishing communication between the interior of said hollow piston rod and the space between the big end of the piston and the end of the cylinder, and the other of said pipes communicating with the space between the cylinder wall and the rod end of said piston, a metering valve, and means for supplying motive uid through said valve at the same pressure simultaneously through said pair of delivery pipes into the spaces on both sides of said piston to produce the desired slow working stroke by means of differential action.

9. A hydraulic power system including a differential reciprocating motor having a piston with a rod end and a big end, means for generating motive uid under pressure comprising a pair of mechanically connected but hydraulically independent pumps, a metering valve, means for directing the motive fluid from one pump at times through said valve simultaneously to both sides of the differential piston, and means for delivering motive fluid under pressure from the other pump, at other times, freely to the rod end only of the piston, independent of said metering valve.

10. A hydraulic power system including a reciprocating motor having a differential piston, a tank, a pair of hydraulically independent pumps both driven by a common prime mover, a metering valve, means for delivering motive Huid under pressure from one of said pumps through said metering valve to both sides of said piston to produce the working stroke by differential action, means for causing the other pump to normally cycle the motive uid idly from the tank back into the tank, and a remotely controlled valve for interrupting this idle cycle and causing said pump to deliver motive uid freely, unrestricted by said metering valve, to one side only of said piston to produce the return stroke.

11. A hydraulic power system including a reciprocating motor having a differential piston with big and rod ends, two hydraulically independent sources of motive uid under pressure, and remotely controlled valve means for supplying uid either from one source to both sides of said piston simultaneously, or from the other source to the rod end only, and at the same time venting uid from the big end.

References Cited UNITED STATES PATENTS 2,078,780 4/1937 Slater -91-31 2,685,276 8/1954 Dyken 91-31 2,907,304 10/1959 Macks 91-31 3,071,157 1/1963 Robertson et al 91-47 3,103,148 9/1963 Brusque 91-417 2,001,716 5/1935 Gardin 91-216 2,274,734 3/ 1942 Pelterie 60`525 2,855,752 10/ 1958 IBrusque 60-52 2,887,092 5/1959 Brady 91-216 FOREIGN PATENTS 356,818 10/ 1961 Switzerland.

PAUL E. MASLOUSKY, Primary Examiner U.S. Cl. X.R. 

